JPS6361793B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a semiconductor device. It is particularly useful when applied to a method of manufacturing a semiconductor laser device. Semiconductor laser devices generally have a double heterostructure with good light confinement in the junction region. This double heterostructure is formed by forming semiconductor layers with a low refractive index and high forbidden band energy on both sides of a so-called active region where laser oscillation or optical modulation is performed. On the other hand, the double heterostructure described above has a difference in refractive index in the vertical direction, but no difference in refractive index in the horizontal direction. Therefore, a buried double heterostructure has been proposed in which a band-shaped mesa is formed on the crystal surface parallel to the heterojunction plane, and a low refractive index semiconductor layer is formed in this mesa region. However, this buried double heterostructure semiconductor laser still has the following drawbacks. That is, when controlling the width of the active region using lithography technology, it is difficult to process with high precision. An object of the present invention is to provide a method for manufacturing a semiconductor device having a semiconductor region, such as an active region, with a fine width. Another object of the present invention is to provide a method for manufacturing a semiconductor device that allows the width of a semiconductor region, such as the width of an active region, to be easily and precisely controlled. The present invention is particularly useful for manufacturing InP-InGaAsP semiconductor laser devices. In this case, it is common to form a double heterostructure using InP as the cladding layer and In _1-x Ga _x As _y P _1-y (0<x<1, 0<y<1) as the active layer. It is. Of course, the same type of InGAsP as the active layer may be used as the cladding layer. Naturally, some impurities may also be contained if necessary. The method for manufacturing the semiconductor laser device of the present invention is as follows. A {100} plane perpendicular to the cleavage plane {011} plane is selected in advance as the substrate surface, and predetermined semiconductor layers are laminated. . When selecting this {100} plane, an inclination of approximately ±5° is practically acceptable. A striped etching mask layer whose length direction is in the <011> direction perpendicular to the cleavage plane is formed on the basic semiconductor surface thus prepared, and at least the active layer is penetrated through this mask. The semiconductor layer is etched until then. In this case, it is essential to use an alcoholic solution containing halogen as the etching solution. By using this etching liquid, an inverted mesa structure can be fabricated with extremely high precision. Next, a semiconductor layer is grown in contact with the longitudinal sides of the inverted mesa structure to embed the inverted mesa structure.
In this way, an embedded double heterostructure is completed. As described above, the striped mask layer in the present invention is formed in such a direction that the substrate surface in the area not covered by the mask layer is easily etched, and the side wall surface extending from the peripheral edge of the stripe into the substrate is difficult to be etched. has been done. When etching begins, the substrate is greatly gouged in the depth direction. but,
The etching speed of the striped sidewall surface is very slow and is hardly etched. Therefore, the cross-sectional shape of the crystal after etching becomes an inverted trapezoid, that is, an inverted mesa structure. Generally, the (011) plane is often used as the cleavage plane in − group compound semiconductors because the (011) crystal lattice plane is composed of the same number of group atoms and group atoms, and is electrically neutral. Therefore, cleavage occurs more easily than the (111) plane. Since the present invention is formed as described above, the active region width is narrower than the stripe width.
Therefore, when carriers are injected from the electrode area,
Carrier concentration occurs in the active region, increasing injection efficiency. That is, since the current density in the active layer becomes high, oscillation with a low threshold current becomes possible. Furthermore, due to the specificity of the chemical interaction between the plane index of the crystal and the etching solution, the width of the active layer can not only be narrowed, but also easily formed to a narrow width below the minimum width for stripe width processing. can. This will be explained in detail below using examples. FIGS. 1a to 1k are manufacturing process diagrams of a semiconductor device as an embodiment of the present invention. FIG. 1a is a cross-sectional view of an n-conductivity type indium phosphide (InP) crystal doped with 1×10 ¹⁸ cm ⁻³ of tin and having a ±5° (100) plane, as viewed from the cleavage surface of the substrate 11. Next, as shown in FIG. 1b, the substrate 11 is
An active layer 102 made of indium galyarsenide phosphide (InGaAsP) is formed thereon by liquid phase growth. As will be described later, it is convenient to separate liquid phase growth into multilayer growth and buried layer formation. The solution composition for growing the first layer is shown in Table 1 as the first solution. After baking the growth furnace at 700°C for 30 minutes, it is once again baked at 630°C for 30 minutes. rear,
The temperature is lowered from 630°C at a rate of 0.47°C/mm for 15 minutes, and the first liquid phase growth is performed at 560°C. Been formed
The InGaAsP layer becomes a quaternary layer that is lattice-matched to the InS crystal of the substrate. Next, as shown in FIG. 1c, the active layer 1 is
A cladding layer 13 made of P conductivity type InP is formed on the cladding layer 13 by liquid phase growth. This liquid phase growth is the second layer of multilayer growth, and the solution composition is shown in Table 1 as the second solution. In addition, the temperature condition for growth is 630℃.
After baking for 30 minutes, the temperature was lowered to 560℃.
Liquid phase growth was carried out at ℃. Next, as shown in FIG. 1d, a cap layer 14 made of P conductivity type InGaAsP is formed on the cladding layer 13 by a third liquid phase growth process. This liquid phase growth is the third layer of multilayer growth, and the composition of this solution is shown in Table 1 as the third solution. The temperature conditions for growth are approximately 617° C. for 1 minute and 30 seconds.

[Table] Next, as shown in FIG. 1e, an oxide film with a thickness of 0.3 μm is deposited on the cap layer 14 by OVD (chemical vapor deposition), and a stripe pattern 107 (hereinafter referred to as stripe) with a width of about 7 μm is formed. layer). The length direction of the stripe layer is selected to be perpendicular to the cleavage plane (011) of the crystalline substrate 11, that is, <011>. Next, as shown in FIG. 1F, using the stripe layer 107 as a mask, the mesa portion 10 is etched with a bromine (Br)-methanol mixture (containing 1% bromine by volume) up to the substrate 11. Form. Due to the direction of the stripes and the unique chemical action of the etching solution, the mesa portion is formed into a so-called inverted mesa structure having an inverted trapezoid. Next, the formation of this inverted mesa will be explained in detail. FIG. 3 is a schematic cross-sectional view of an experimental sample used to explain the inverted mesa structure of the present invention. After the above-described liquid phase growth is performed on the InP crystal substrate 41 whose surface is the (100) plane, a CVD oxide film 47 is formed on the entire surface. Various rectangular windows were formed in this oxide film 47 as shown, and etching was performed through these windows. For the above Br-methanol based etching solution,
The substrate 41 exhibited different etching patterns depending on the surface index. In particular, when etching a (111) plane, for example, the (111) plane velocity is
It was observed that it was extremely small, 1/10 to 1/100 of the surface. It has been found that because the etching is performed sequentially in the depth direction, there are cases in which grooves are formed in the window in a diverging shape as shown in the figure, and in cases in which a V-shaped groove is formed. Particularly in the former case, when two windows are placed adjacent to each other in parallel, an inverted mesa structure 40 is formed in the middle region. Therefore, if a stripe layer with a predetermined width is formed in advance using, for example, an oxide film, and this stripe layer is arranged as a cleavage plane perpendicular to, for example, the (011) plane, an inverted mesa structure can be easily formed. . As an etching solution, the above-mentioned Br-ethanol mixed solution was effective up to a Br volume ratio of 0.05 to 10%, but 0.1 to 5% was the best at room temperature.
This is because the solution itself is volatile, so if the amount of Br is too large or too small, etching will not be successful. That is, if the volume ratio of Br is less than 0.1%, (1) firstly, as mentioned above, the overall concentration of the solution is likely to further decrease due to volatilization of Br; and (2) the etching rate is 0.01 μm/ This is not desirable because it loses its practicality as an etching over time. Furthermore, when the Br capacity ratio exceeds 5%, the etching directly under the mask (generally side etching) becomes rapidly faster, reaching 1/3 or more of the etching speed in the depth direction. This extremely hinders the control of the width of the active layer and makes it impractical. Further, as this etching solution, a mixed solution of a halogen element and alcohol is effective. Bromine (Br), iodine (I), etc. can be used as the halogen. Furthermore, if a few percent of a hydrogen halide such as HBr or water is added to the Br-methanol mixture, the etching rate will be increased. Furthermore, as the alcohol, in addition to the above-mentioned methanol, ethanol, isopropyl alcohol, etc. can be similarly applied. The solution temperature during etching is
A temperature of 10°C to 30°C may be used. It is generally sufficient to carry out the reaction at room temperature. FIG. 1F shows an inverted mesa structure 10 formed as described above. After etching for about 7 minutes, the active layer 102 has a width of 1.0-1.5 .mu.m, forming an extremely narrow active region 12. That is, it can be formed to have a width of 1/4 to 1/6 of the stripe layer 107. Moreover, although the width of the active region 12 is extremely narrow, the crystal surface of the cap layer 14 has a width of 6 μm.
This results in a relatively wide stripe with a width of m, which is extremely convenient for electrode formation. Next, as shown in FIG. 1g, a first buried layer 15 made of InP is formed by liquid phase growth on the substrate 11 exposed by the etching.
This liquid phase growth corresponds to the formation of the first layer of buried growth, and the solution composition is shown as the first solution in Table 2. This crystal growth is carried out at 560° C. according to the usual liquid phase epitaxial growth method. Next, as shown in FIG. 1h, a second buried layer 16 made of n-conductivity type InGaAsP is formed on the first buried layer 15 by liquid phase growth. Crystal growth of the second buried layer 16 starts at 617°C. In the figure, it is drawn to be horizontal to the cap layer 14, but it is not necessarily limited to this shape.

Next, as shown in FIG. 1i, an oxide film 117 is formed over the entire surface of the second buried layer 16 and cap layer 14 by CVD. Next, as shown in FIG. 1J, the oxide film 1 is
17, a diffusion window 104 is formed in accordance with the pattern of the stripes 107 by ordinary photolithography.
form. Then, through the window 104,
Diffuse Zn using the sealed tube method using ZnP ₂ as a source. The diffusion temperature at this time was 550℃, the diffusion time was 5 minutes,
The depth of the diffusion layer 114 is approximately 1 μm. Next, as shown in FIG. 1k, the back surface of the crystal substrate 11 is polished and etched to a thickness of 100 μm.
After thinning the film to about m, Cr/Au is deposited on the diffusion layer 114 and oxide film 127 on the surface p conductive side at room temperature.
Conductive film 18, Au/Sn (10
%) A conductive film 19 is deposited to form an ohmic electrode. Finally, the chip is divided into chips with a cavity length of 300 μm by cleavage, and bonded to a Cu heat sink using Sn to form a semiconductor laser device (not shown). FIG. 2 shows a schematic cross-sectional view of a semiconductor laser formed according to the above embodiment. The active layer 2 has a thickness of
Lattice matching is achieved with the crystal substrate 1 with a width of 0.3 μm and a width of 2 μm.
Moreover, the oscillation wavelength is adjusted to 1.3 μm. The thickness of the p-InP cladding layer 3 is approximately 2 μm. The thickness of the p-InGaAsP cap layer 4 is approximately
The thickness of this layer is 0.5 μm, and the composition of this layer is adjusted so that it has lattice matching with the substrate 1 and has a peak emission wavelength of about 1.2 μm. In this laser element, the threshold current value is 67mA (threshold current density is
9KA/cm ² ), and the differential quantum efficiency was 23%. In conventional rib structures (in which the buffer layer directly under the active region has a concave or convex shape) and planar stripe structures, the threshold current value was 150 mA and the differential quantum efficiency was approximately 15%. In the heterostructure, the threshold current value is reduced to about 1/3 of the conventional value.
Additionally, the differential quantum efficiency was improved by approximately 2/3 times. According to the manufacturing method of the present invention, the threshold current value can be set to 20 mA in the case of pulse operation. FIG. 4 is a schematic cross-sectional view of a semiconductor laser device showing another embodiment of the present invention. The above-mentioned FIG. 1 1f
After the mesa etching process shown in , p-conductivity type InP is grown by liquid phase growth to approximately the height of the active layer 52.
Form layer 551. Next, n is formed on the layer 551.
A conductive type InP layer 552 is formed by liquid phase growth to approximately the height of the cladding layer 53. That is, a PN junction is formed in the first buried layer 15 shown in FIG. 1f above. Thus, when a PN junction is formed within the buried layer, leakage current is prevented from occurring within the buried layer during operation of the laser element. FIG. 5 is a schematic cross-sectional view of a semiconductor laser device showing still another embodiment of the present invention. The first mentioned above
After the substrate preparation step shown in FIG. 1a, a buffer layer 601 (sometimes called a cladding layer) of n-conductivity type InP is formed by liquid phase growth. Next, active region 62 and cladding layer 63 are formed as shown in the previous embodiment. Next, a cap layer 64 of In _1-x is formed on the cladding layer 63.
Ga _x As _y P _1-y (x=0.16, y-0.36) is formed by a 0.5 μm liquid phase epitaxial growth method. Next, an oxide film with a stripe width of 7 μm is formed and etched. In the semiconductor laser thus formed, the width of the active layer 3 can be made 1.5 μm with good reproducibility. The width of the active region needs to be at most 2 μm for fundamental axis mode oscillation, and the narrower the better. Considering that the width of conventional wiring patterns was limited to 2 to 3 .mu.m due to processing accuracy, it can be seen that the narrow active region width of the present invention can only be achieved by an inverted mesa structure.
In the case of mesa etching in this example, etching is performed up to the buffer layer 11. When a buffer layer is formed on the surface of the substrate 61 in this manner, an active layer 62 with a low dislocation density can be formed. In the above embodiments, only a buried heterostructure laser has been described, but it goes without saying that the present invention is not limited to this and can be applied to forming an inverted mesa and other mesas. That is, it can be applied to the manufacture of semiconductor devices using InP crystals and semiconductor devices in which other − group compound semiconductor layers are formed on InP crystals.

[Brief explanation of drawings]

FIG. 1 is a manufacturing process diagram of a semiconductor device as an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of a semiconductor device formed by the manufacturing method of the present invention, and FIG. 3 is a diagram showing the manufacturing method of the present invention. Schematic cross-sectional view of the sample used for this purpose. FIG. 4 is a schematic sectional view of a semiconductor device formed according to another embodiment of the present invention, and FIG. 5 is a schematic sectional view of a semiconductor device formed according to still another embodiment of the invention. 1...Crystal substrate (InP), 2...Active region (InGaAsP), 3...Clad layer (InP), 4...
Cap layer (InGaAsP), 5...buried layer (InP), 6...buried layer (InGaAsP), 7...oxide film layer, 8, 9...metal electrode, 10...inverted mesa structure.

Claims (1)

[Claims] 1. A semiconductor substrate having a substantial {100} plane of InP crystal on its surface, or a semiconductor substrate on which at least one semiconductor layer is grown. When a mask is formed and the longitudinal direction of this striped mask is the {100} plane of the semiconductor surface on which the mask is placed, the relationship is in the <011> direction, and then bromine is added at a volume ratio of 0.1% to 5%. 1. A method for manufacturing a semiconductor device, characterized in that a semiconductor layer having an inverted mesa structure is obtained by etching using an alcohol solution containing the same. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the bromine-containing alcohol solution further contains hydrogen halide or water.